Adds package version file

It's used by find_package() to handle versioning.

CMakeLists.txt

@@ -3,6 +3,7 @@ cmake_minimum_required(VERSION 3.0.2 FATAL_ERROR)
 project(qtermwidget)
 
 include(GNUInstallDirs)
+include(CMakePackageConfigHelpers)
 include(CheckFunctionExists)
 
 set(LXQTBT_MINIMUM_VERSION "0.3.0")
@@ -174,6 +175,17 @@ if(APPLE)
     set_target_properties(${QTERMWIDGET_LIBRARY_NAME} PROPERTIES INSTALL_NAME_DIR ${CMAKE_INSTALL_FULL_LIBDIR})
 endif()
 
+write_basic_package_version_file(
+    "${CMAKE_BINARY_DIR}/${QTERMWIDGET_LIBRARY_NAME}-config-version.cmake"
+    VERSION ${QTERMWIDGET_VERSION}
+    COMPATIBILITY AnyNewerVersion
+)
+
+install(FILES
+    "${CMAKE_BINARY_DIR}/${QTERMWIDGET_LIBRARY_NAME}-config-version.cmake"
+    DESTINATION "${CMAKE_INSTALL_DATADIR}/cmake/${QTERMWIDGET_LIBRARY_NAME}"
+    COMPONENT Devel
+)
 install(TARGETS ${QTERMWIDGET_LIBRARY_NAME} DESTINATION "${CMAKE_INSTALL_LIBDIR}")
 install(FILES ${HDRS_DISTRIB} DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}/${QTERMWIDGET_LIBRARY_NAME}")
 # keyboard layouts